1. Field of the Invention
The present invention relates to a controller for an elevator system having at least one elevator shaft and in which two elevator cars are in service in each shaft.
2. Description of Related Art
In general, an elevator system has one elevator car in each elevator shaft. There has been proposed, however, an elevator system having two elevator cars in each shaft.
For a conventional elevator system including multiple elevator cars and elevator shafts with a single elevator car in each shaft, xe2x80x9cgroup supervisory controlxe2x80x9d is usually used to control assignments of particular elevator cars to respond to calls at floors served by the elevators. Group supervisory control has also been proposed for an elevator system in which two cars are in service in each shaft. In this case, however, control to avoid a collision between cars in service in the same shaft is required. Group supervisory control units with a collision avoidance feature have been proposed in Japanese Unexamined Patent Publications Hei. 9-272662 and Hei. 8-133611.
Japanese Unexamined Patent Publication Hei. 9-272662 discloses a xe2x80x9cropelessxe2x80x9d elevator system in which elevator cars can be moved vertically and horizontally. An elevator car having no call to which to respond is stopped or moved to the side in a shaft to avoid a collision with a car traveling vertically in the shaft.
Japanese Unexamined Patent Publication Hei. 8-133611 discloses setting aside a section of a shaft only for a certain elevator car and prohibiting entry of another car in this section. A controller is provided to stop another elevator car from entering the section set aside.
The prior art techniques described above pose the following problems.
The group supervisory controller described in the former publication is not effective for a system that is incapable of moving to a side path an elevator car not assigned to respond to a call. Furthermore, if an elevator car having no call is not moved to a side path, then that car is simply stopped in the shaft, making efficient operation of the cars impossible.
The group supervisory controller disclosed in the latter publication stops an elevator car not assigned to respond to a call by assigning a provisional call to the elevator car before a no-entry section of the elevator shaft is reached, making efficient operation of the elevator cars impossible.
The present invention has been made with a view toward solving the problems described above, and it is an object of the present invention to provide an elevator system controller and method producing more efficient group supervisory control of an elevator system including two elevator cars in each elevator shaft while avoiding a collision between elevator cars.
According to one aspect of the present invention, there is provided an elevator system controller for controlling an elevator system including a plurality of elevator shafts and two elevator cars in service in each shaft comprising a risk calculating unit for calculating risk of a collision between two elevator cars in a single elevator shaft when one of the elevator cars is responding to a new call for service; a car assigning unit for assignment of an elevator car to respond to the new call based on the risk of a collision; and an operation control unit for controlling operation of the elevator cars based on the assignment by the car assigning unit.
In a preferred form, the risk calculating unit calculates, for each elevator car in the elevator system, probability of a collision between elevator cars in a single shaft as the risk; calculates a possibility of withdrawal of a second car in an elevator shaft including first and second elevator cars, to a location where no collision will occur, when the first elevator car has a risk of collision larger than a threshold value; and recalculates the risk of collision of the first and second elevator cars in the elevator shaft based on the possibility of withdrawal of the second car to the location where no collision will occur.
In another preferred form, the car assigning unit deletes the first elevator car from potential assignment for response to the new call if the first elevator car has a risk of collision larger than the threshold value and if the second car cannot be withdrawn to the location where no collision will occur.
In yet another preferred form, the possibility of withdrawal of the second elevator car to the location where no collision will occur is based on a predicted arrival time of each of the elevator cars in the elevator system at a floor where the new call has been issued.
In a further preferred form, the car assigning unit assigns an elevator car to respond to the new call based on an evaluation index that includes at least waiting time for arrival of an elevator car in response to the new call, prediction error, and passenger load in a car, in addition to the risk of collision.
In a still further preferred form, the elevator system controller comprises a traffic condition determining unit for determining traffic condition of the elevator system, and wherein the operation control unit forwards some cars to floors to pause, based on the traffic condition.
According to a second aspect of the invention, a method of controlling an elevator system including a plurality of elevator shafts and two elevator cars in service in each shaft comprises calculating risk of a collision between two elevator cars in a single elevator shaft when one of the elevator cars responding to a new call for service; assigning an elevator car to respond to the new call based on the risk of a collision; and controlling operation of the elevator cars based the elevator car assigned.
In a preferred form, the method includes calculating, for each elevator car in an elevator shaft, probability of a collision between elevator cars in a single shaft as the risk; calculating a possibility of withdrawal of a second car in an elevator shaft including first and second elevator cars, to a location where no collision will occur, when the first elevator car has a risk of collision larger than a threshold value; and recalculating the risk of collision of the first and second elevator cars in the elevator shaft based on the possibility of withdrawal of the second elevator car to the location where no collision will occur.
In another preferred form, the method includes deleting the first elevator car from potential assignment for response to the new call if the first elevator car has a risk of collision larger than the threshold value and if the second car cannot be withdrawn to the location where no collision will occur.
In a further preferred form, the method comprises basing the possibility of withdrawal of the second elevator car to the location where no collision will occur on a predicted arrival time of each of the elevator cars in the elevator system at a floor where the new call has been issued.
In yet another preferred form, the method comprises assigning an elevator car to respond to the new call based on an evaluation index that includes at least waiting time for arrival of an elevator car in response to the new call, risk prediction error, and passenger load in a car, in addition to the risk of collision.
In still another preferred form, the method comprises determining traffic condition of the elevator system and forwarding some cars to floors to pause, based on the traffic condition.